According to biologist Stephen Palumbi (2001), humans are the “world’s greatest evolutionary force.” What Palumbi means is that we humans, like no other species before us, have had a profound effect on the evolutionary histories of almost all forms of life, including the potential to alter global ecology and destroy ourselves and much life on earth. Even massive geological events and mass extinctions did not wreak the havoc that may result from modern human technology.
The geological record indicates that in the last 570 million years, there have been at least 15 mass extinction events, two of which altered all of the earth’s ecosystems (Ward, 1994). The first of these occurred some 250 mya and resulted from climate change that followed the merging of all the earth’s landmasses into one supercontinent. The second event happened around 65 mya and eradicated tens of thousands of species, including most dinosaurs (recall from Chapter 5 that birds are their living descendants).
A third major extinction event, perhaps of the same magnitude, is occurring now, and according to some scientists, it may have begun in the late Pleistocene or early Holocene (Ward, 1994). Unlike all other mass extinctions, this one hasn’t been caused by continental drift or collisions with asteroids. Today it’s due to the activities of a single species, Homo sapiens.
The overall effects of human activities, particularly in the last 250 years, have had such a profound effect on the earth that many scientists are now recognizing these sudden and dramatic changes as marking a new geological era, called the Anthropogenic (Vince, 2011). As an example of just how much our species has altered the planet, one current estimate suggests that as much as 43 percent of terrestrial habitats have been transformed to either agricultural or urban landscapes (and this does not include roads outside urban areas) (Basnosky et al., 2012). Like earlier major shifts in the earth’s geology and biodiversity, the Anthropocene is comparable to the two planetary events mentioned above. These, however, were caused by gigantic asteroid collisions or super volcanoes; the Anthropocene (“the age of humans”) is the result of human behavior.
For at least the past 15,000 years, human activities such as hunting and clearing land for cultivation have taken their toll on nonhuman species, but species are currently disappearing at an unprecedented rate. Hunting, which occurs for reasons other than acquiring food, is a major factor. This is particularly true for nonhuman primates, tigers, elephants, and rhinoceroses. As you saw in Chapter 6, aside from being hunted for food, nonhuman primate and tiger body parts are widely used in traditional medicines, mainly in Asia, and infant animals are commonly funneled into the exotic pet trade. Rhinoceros horns are also popular in parts of the Middle East, especially as knife handles, and in Asia for medicinal purposes. And there has been an enormous resurgence of elephant hunting in Africa for their ivory tusks. Competition with introduced non-native species—such as pigs, goats, and rats—has also contributed enormously to the problems that wild animals face (Fig. 17-6). But in most cases the most important cause of extinction is habitat reduction.
Habitat loss is a direct result of the burgeoning human population and the resulting need for building materials, grazing and agricultural lands, and ever-expanding human habitations (Fig. 17-7). We’re all aware of the risk to such highly visible species as elephants, pandas, rhinoceroses, tigers, and mountain gorillas, to name a few. These risks are real, and within your lifetime, some of these species will certainly become extinct. But the greatest threats to biodiversity are to the countless unknown species that live in the world’s rain forests and in the oceans (particularly coral reefs).
Should we care about the loss of biodiversity? If so, why? In truth, many people don’t seem to be very concerned, and this may be because these topics aren’t extensively covered in most media. What’s more, when people explain why we should care, they usually point out the benefits (known and unknown) that humans may derive from wild species of plants and animals. An example of such a benefit is the chemical taxol (derived from the Pacific yew tree), which may be an effective treatment for ovarian and breast cancer. These benefits are important, but preserving biodiversity for its own sake is every bit as crucial.
The United Nations recently organized another large international conference to address pressing issues concerning biodiversity. The conference (an extension of the Convention on Biological Diversity) took place in October 2010 in Nagoya, Japan, and was attended by representatives from 193 countries. Unlike the lack of agreement that characterized the conferences focusing on global climate change, the results of the biodiversity meeting were quite encouraging. Conference members agreed to increase cooperation and to share financial benefits that come from the development of new drugs from wild plants and animals. What’s more, they produced an impressive list of significant international goals to be reached by 2020, including an effort to reduce to half or bring close to zero the rate of loss of all natural habitats, to reduce pollution to levels that are not detrimental to ecosystems and biodiversity, to conserve at least 17 per cent of terrestrial areas and 10 percent of coastal and marine areas in protected zones, to prevent the extinction of known threatened species, and to restore at least 15 percent of degraded ecosystems.